For over five decades antimicrobial resistance has presented and remains a major healthcare problem throughout the world, largely due to the indiscriminate use of antibiotics. This liberal usage of antibiotics is partially driven by the clinicians' need to ensure adequate empiric coverage in the face of diagnostic uncertainty and the availability of a small window of opportunity for treatment. Currently, the selection of antimicrobials effective against infectious pathogens is typically performed by first recovering, culturing, and identifying the microorganism(s) from specimens and then testing the susceptibility of these pathogens against various antibiotics over a range of concentrations. Conventional antimicrobial susceptibility tests (AST) are typically performed in suspension assays (e.g., broth microdilution assay) or in agar plate assays (e.g., disk diffusion assay) and take 1 to 3 days. While this process is underway, a wide-ranging treatment regimen is usually adopted based on a number of clinical parameters, local epidemiology, and the suspected causative pathogens. However, it is common for such broad-spectrum treatment to fail, cause adverse effects, or lead to antibiotic resistance and other health issues, such as unacceptable mortality and morbidity, with significant economic and health care ramifications.
It is now established that faster availability of susceptibility data can enable physicians to initiate or switch to an appropriate antimicrobial therapy sooner, thus reducing health care costs due to fewer laboratory tests, invasive procedures, or the length of hospital stay. While there has been some progress in recent years for rapid determination of antibiotic susceptibility, the tests that are currently available are either limited to a few selected organisms, do not reliably predict drug response, or are cost-prohibitive to a significant portion of the population even in developed countries.